10 November 2009

Alternative Hypotheses About Climate Change

A distinguished group of nineteen AGU Fellows (names below) have published an article in EOS (PDF, AGU membership required) in which they present three competing hypotheses about climate change, only one of which can be true. Which one do you think is correct?
Humans are recognized as having a major role in influencing environmental variability and change, including their influence on the climate system. To advance scientists’ understanding of the role of humans within the climate system, there remains a need to resolve which of the following three hypotheses is correct:

Hypothesis 1: Human influence on climate variability and change is of minimal importance, and natural causes dominate climate variations and changes on all time scales. In coming decades, the human influence will continue to be minimal.

Hypothesis 2a: Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and involve a diverse range of first- order climate forcings, including, but not limited to, the human input of carbon dioxide (CO2). Most, if not all, of these human influences on regional and global climate will continue to be of concern during the coming decades.

Hypothesis 2b: Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and are dominated by the emissions into the atmosphere of greenhouse gases, the most important of which is CO2. The adverse impact of these gases on regional and global climate constitutes the primary climate issue for the coming decades.

These hypotheses are mutually exclusive. Thus, the accumulated evidence can only provide support for one of these hypotheses. The question is which one?
In a coming post, I'll give their answer and why they think it matters. Meantime, what do you think?

The authors are:

ROGER PIELKE SR., University of Colorado, Boulder;
KEITH BEVEN, Lancaster University, Lancaster, UK;
GUY BRASSEUR and JACK CALVERT, National Center for Atmospheric Research, Boulder, Colo.;
MOUSTAFA CHAHINE, Jet Propulsion Laboratory, California Institute of Technology, Pasadena;
RUSSELL R. DICKERSON, University of Maryland, College Park;
DARA ENTEKHABI, Massachusetts Institute of Technology, Cambridge;
EFI FOUFOULA- GEORGIOU, University of Minnesota, Minneapolis;
HOSHIN GUPTA, University of Arizona,Tucson;
VIJAY GUPTA, University of Colorado;
WITOLD KRAJEWSKI, University of Iowa, Iowa City;
E. PHILIP KRIDER, University of Arizona;
WILLIAM K. M. LAU, NASA, Greenbelt, Md.;
JEFF MCDONNELL, Oregon State University, Corvallis;
WILLIAM ROSSOW, City College of New York, New York;
JOHN SCHAAKE, U.S. National Oceanic and Atmospheric Administration, Silver Spring. Md.;
JAMES SMITH, Princeton University, Princeton, N. J.;
SOROOSH SOROOSHIAN, University of California, Irvine;
ERIC WOOD, Princeton University


Brendan said...

Only 2a can be true.

Ben said...

My guess is "We don't know which is correct."

Maurice Garoutte said...

Number one.

And let’s get on with it. My three year old grand daughter depends on me getting it right.

Skip said...

They completely miss 2c:

"Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and involve a diverse range of first- order climate forcings, including, but not limited to, the human input of carbon dioxide (CO2). However, the combined total is well within historical norms, and is not of any particular concern or danger."

2a is closest to that, but not exactly. So I'd have to go with 'none of the above' as stated.

Roger Pielke, Jr. said...


How is your 2c different than 1?

If the "combined total is well within historical norms, and is not of any particular concern or danger" then this is the same as saying "Human influence on climate variability and change is of minimal importance, and natural causes dominate climate variations and changes on all time scales", no?

Sylvain said...

Anyone who reads your father's blog knows that the answer is 2a.

Any policy that would be based on 2b is doom to fail in any length of time, for both local and world wide scale.

Sharon F. said...

Roger, not being a climate person I can't distinguish between 2 a and 2 b, whether it is "of concern" or the "primary climate issue." What other issues are on the table for consideration at "primary"?

Roger Pielke, Jr. said...


Stay tuned ... I'll soon (tomorrow) post up their answer to their question and why they say it matters.

Amir Netz said...

I think we do influence the climate, but mostly through urbanization and deforestation. CO2 emissions are not a significant factor. Looking at the long range trends, it is pretty clear that most of the warming we are seeing is just a natural part of the long term defrosting from the ice age.

I also don't subscribe to the theory of positive feedbacks meaning that there is not going to be any "run-away" abrupt climate change. Temperatures will rise in the range of 1.5C/century. Such warming is mostly beneficial, so I see no cause for alarm.

I guess that makes me a H(1) person?

Skip said...

Roger it differs from 1 in that it acknowleges that human activity may be affecting climate quite measurably. It just says that this isn't a big deal. Perhaps I'm misreading hypothesis one, my paraphrase of it is 'human activity simply isn't affecting climate to any particular amount'. In any case, those do seem to be 2 different cases, where we're affecting the climate but it's not a problem, and the case where we're not significantly affecting the climate.

Roger Pielke, Jr. said...


Yes, I see your point. But #1 says "minimal importance" which I interpret as "not a problem".

Steve Reynolds said...

"Anyone who reads your father's blog knows that the answer is 2a."

I agree with that and the 2a answer.

SBVOR said...


With your father involved, the obvious answer is Hypothesis 2a.

But -- based upon a preponderance of the evidence -- I choose Hypothesis 1.

I think history will find this paper to have been a pivotal moment in proving me correct.

As I stated in this recent post:

“[B]ased upon what we know about historic CO2 levels, my bet is that the Iris Effect which Dr. Lindzen has long hypothesized and which this study demonstrates is -- indeed -- a big part of the explanation for why CO2 levels at about 20 times current levels did NOT cause runaway catastrophic global warming 520 million years ago.

This study and, at least one other (abstract here) support this Iris Effect hypothesis. There may well be others I am unaware of.

This question of how water vapor responds to the tiny amount of warming directly caused by CO2 has always been the linchpin of climate change theory.”

Anyone selecting either 2a or 2b might be well advised to reconsider any human contributions to warming which rely upon water vapor as an amplifying forcing factor in order to be relevant.

The jig is (almost) up.

Mike said...

If dependent upon public, grant-based tax-generated funding for subsequent research dollars I would suspect that the authors would espouse hypothesis 2b.

"The adverse impact of these gases on regional and global climate constitutes the primary climate issue for the coming decades."

If only I could submit a similar statement during my next performance review. I could then justify my employment indefinitely!

Peer-reviewed, scientifically-viable research aimed at long-term job security. The answer could be just another "genious grant" away from realization.

Geckko said...

I have seen to date no compelling reason to reject H1.

Geckko said...

Just to clarify, it is the final sentance of H2a, which is a little non sequitur, that I don't yet find proven.

Unless by "continue to be of concern", you mean "people will still worry about it", rather than "will have a material adverse affect".

If that is the proper interpretation I could reject neither H1 nor H2.

Note that this is contradictory. YOu switch between "importance" and "significant".

Human influence can be "significant" (land use, GHG forcing etc. has a measurable affect on temp say), but it is not "important" - nor reason to believe it will cause significant adverse net costs.

Note tha H! stipulate "importance", while H2a stipluates "significant" (as in "the human influences are significant")

jgdes said...

The interesting thing about option 1 is that it would never be proposed by anyone whose job depended on there being significant human influence on climate; iow turkeys don't vote for Christmas.

For a proper study, all evidence, such as it is, would need to be independently reviewed for the most likely scenario to be properly ascertained. That independent body would need to be free from people who would benefit from carbon limitations or climate-related grant awards. I wonder if that excludes the self-appointed panel above.

Hence while surely this panel chose 2a, the most likely conclusion imo should be that proper analysis of the very sparse data doesn't yet justify any conclusion different from 1, with the caveat that 2a is still plausible, needs monitored, and that such human influence could be beneficial, detrimental or both.

The most important conclusion though that anyone should reach is that long-term climate prediction is very crude and biased guesswork and will remain so for a long time yet. Therefore any policy decision should be prudent and recognize the very real possibility of doing more harm than good. It goes without saying that any impacts reports based on model projections are largely worthless: That much isn't even in dispute by climate modelers.

lkdemott said...

I think the answer is obvious. There is not sufficient evidence to rule out any of these competing hypotheses.

Bob Tisdale said...

Roger: Hypothesis 1 is correct.

Climatologists misunderstand (or misrepresent) the multiyear aftereffects of significant traditional El Nino events (those that aren’t counteracted by volcanic eruptions). There were only two that fit that profile since the late-1970s-early 1980s, and those El Nino events (1986/87/88 and 1997/98 El Ninos) created upward step changes in TLT and SST anomalies for major portions of the globe. These step changes are not acknowledge by climatologists who insist the relationship between ENSO and global temperature is linear. But the instrument temperature record indicates otherwise--that the relationship is non-linear and that the lingering effects of those two El Nino events are responsible for much of the rise in temperatures over the past two decades. Refer to my post:

Don't let the title of the post concern you. The discussion deals primarily with the multiyear effects of those specific El Nino events


edaniel said...

We don't yet know.


The available data are not sufficient to allow differentiation between all the sources of the potential drivers for climate change.

The available data are frequently incorrectly interpreted. Causality, the important physical phenomena and processes, are very frequently ( almost always ) omitted from analyses of the available data. The data-analysis methods, and the data itself, are frequently not Verified.

The measured physical quantity ( some kind of average temperature near the surface ) does not correspond to the theoretical quantity of interest ( the radiative-equilibrium temperature of the Earth ). The daily and seasonal variations of the temperature of the atmosphere near the Earth's surface are sufficiently large so as to negate the thermodynamic foundations of a simple 'average temperature'.

Perturbations large in temporal and spatial scale which cause significant redistribution of the energy content of the Earth's systems are sufficient to confound interpretations of measured estimates of the temperature near the surface. These redistributions of energy can cause false both increases and decreases in energy content.

The mathematical models are (1) incomplete relative to accounting for all potential sources of drivers of climate change, (2) not yet capable of sufficient either temporal or spatial resolution, (3) the models and coding has not yet been Verified, (4) many of the mathematical models have not yet been Validated, (5) no Independent agency has undertaken any detailed investigations into the models, methods and coding, (6) produce fuzzy numbers which are additionally evaluated in a fuzzy manner.

The time scale ( 100 years ) on which attention is focused is not in accord with the theoretical basis of the actions of a radiative imbalance due to accumulation of CO2 in the atmosphere; it's at least an order of magnitude too short. The radiative-equilibrium concept itself does not obtain for the Earth's systems.

While the radiative energy transport response of a homogeneous mixture of inert pure gases is well established, the Earth's atmosphere is not such a mixture. The Earth's atmosphere is a multi-component, multi-phase mixture of gases, vapors, liquids, and solids.

While the radiative energy transport response of various solid surfaces is well established, the Earth's surface is not among these.

Many of the significant nitty-gritty interactions between the subsystems of the Earth's total system have yet to be considered.

Howard said...


I don't think that a certain doubling or trippling of CO2, deforrestation and irrigated agriculture can be termed minimal., even with non-positive feedback. Not catastrophic, yes.

Leonard Weinstein said...

I think 1 is a bit weak, but 2a and 2b are both too strong. The effect of deforestation and land management combined with particulate pollution are probably significant but not dominating. If the only question is about CO2 and methane, 1 ia probably closest, but the possibility of some measureable effect (but second order) is likely.

Malcolm said...

1b. The recent warming and cooling over the past 30 years would indicate that natural and truly global variations in climate are of greater significance than man-made contributions to climate which are at the moment land based and localised.

Sharon F. said...

I think Mike has a point.. but I wonder if there are any scientists left standing (who would understand the topic) who are not currently funded to some extent by the profusion of climate funds?

PaulM said...

Roger, I don't think anybody is in suspense, the answer given by those authors is going to be 2a.

Although only one of them can be true, it does not follow that one of them is true. I would go for skip's 2c (which IS different from 1) or Malcolm's 1b. But if forced to select one of the three I would go for 1.

Andrew said...

11-"But #1 says "minimal importance" which I interpret as "not a problem"."

See, here is your problem. Even if 2b were true that doesn't mean that the effect is a "problem". It means it is "important". Heck, it could be a good thing. None of the hypotheses address the question of whether the effects are "problems".

Canada Guy said...

Everyone knows that preventing climate change, or at least the worst consequences of it, is not going to be easy. While the task required is large and difficult, there are some simple, quick, and easy fixes that can make a real difference, and perhaps even buy us more time. But they are being ignored.


SBVOR said...

-24-Sharon F,

I am a scientist (trained in a related field). I am “still standing”. I “understand the topic”. I have never received one dime from any energy company. I do not own any energy stocks. And -- most importantly -- I have never received any government funding to study climate change (and don’t expect to). Frankly, I think that makes me among those who can be most trusted to evaluate the fundamentals of the science accurately and objectively.

Professor Carter asserts that governments around the world have poured $50 billion into this particular gravy train (dwarfing -- by FAR -- any funds from ExxonMobil).

I think many climate scientists sense that the CO2 gravy train is fast approaching its final station. It’s been a really cushy and profitable ride. Some have even sought and achieved near rock star fame. Now, they’re looking for a new set of gravy trains to climb aboard (while riding this one as far as they can).

H.L. Mencken said:
“The urge to save humanity is always a false front for the urge to rule it.”

That explains the motivation of the (totalitarian Socialist) politicians. Climate scientists are far from immune from a financial motivation. And, some are more politician (and celebrity) than scientist.

Dean said...

Yes, we all know which one the Pielke's think is accurate. But I don't see 2a and 2b as mutually exclusive. Your father doesn't consider CO2 a non-issue, just an exaggerated one, as I understand it. IPCC doesn't consider land use and other non-CO2 aspects to be nonissues.

It seems to be an issue of degree, and not fundamental between 2a and 2b.

And I would add that policy at this point should address that which is cheapest, easiest, and gains the most in avoided atmospheric forcing, whether or not the component of AGW connected with it is dominant or not. Efficiency upgrades seem to fit that category, and I think they address CO2 more than other factors.

Roger Pielke, Jr. said...


The authors' certainly don't see 2a and 2b as overlapping!

Sharon F. said...

It sounds like an emphasis issue.. are greenhouse gases one of many things that will all be potentially worrisome, or the preeminent factor that influences climate as in "dominated" and "primary" climate issue. Based on your words, but of course we could quantify..

Say you had worry on a scale of 1--10. With 1 barely worried and 10 very very very worried.

Sounds like 2A's would give a variety of forcing causes a 6, while 2Bs would give greenhouse gases a 10+ and all others 0. So I am with Dean on it may be a matter of degree. Because you could imagine people who are 10-9-9.. (don't know how many total sources of forcing there are).

Of course, then if you knew the total sources (which you do) you could calculate a total climate worry factor, the sum of each worry factor of an individual source.

Jason S said...

Dean et al:

If climate change is not dominated by anthropogenic emissions, then action to curb anthropogenic emissions is not sufficient to address the issue.

SBVOR said...

-32-Jason S,

Right you are (as usual)! But…

/Sarcasm on/

If we really want to get serious about creating -- for the first time in the entire history of the planet -- a stable climate, we will have to start with eliminating those pesky Milankovitch cycles.

Then -- given that multi-million year ice house conditions (such as the present one) may well be caused by some anomaly in our solar system’s rotation about the galaxy -- we will next have to look into “fundamentally transforming” the galaxy.

It won’t be easy and it won’t be cheap. But, it’s a small price to pay in order to realize the utopian vision of “New America”!

/Sarcasm off/

Dean said...

Jason - The 2a statement above includes CO2 as a "first order climate forcing". Thus addressing it will help, though not be enough to solve the problem.

Keith said...

".....including their influence on the climate system."
Please define "climate system". I can then contemplate the alternative hypotheses.
Please draw a boundary, and indicate what is inside the climate system and what is outside.

Roger Pielke, Jr. said...


From the IPCC glossary:

Climate system

The climate system is the highly complex system consisting of five major components: the atmosphere, the hydrosphere, the cryosphere, the land surface and the biosphere, and the
interactions between them. The climate system evolves in time under the influence of its own internal dynamics and because of external forcings such as volcanic eruptions, solar variations, and human-induced forcings such as the changing composition of the atmosphere and land-use change.


Andrew said...

Dean-you are repeating the same fallacy as Roger (who just ignored this point, sadly). You say:

"The 2a statement above includes CO2 as a "first order climate forcing". Thus addressing it will help, though not be enough to solve the problem."


This is apparently difficult to grasp. These hypotheses have nothing to do with whether there is a "problem" at all, then are about the factors which contribute to climate change.

What you are doing is assuming that if there is climate change from CO2 and other human climate forcings, that is a problem. Regardless of whether there is one or not IT DOES NOT FOLLOW THAT IT IS FROM THESE HYPOTHESES ALONE!

I grow weary of battling this endless tide of non sequitor.

jgdes said...

I agree with Dean, if we are potentially perturbing the system then some action can be justified but only action which saves us money in the short to medium term is sensible or workable. Happily there is a lot of good green tech which can or could do that at minimal real cost. Statements to the contrary can almost always be sourced back to pure disinformation.

Long term we need enough energy for 9 billion people by 2050 so all energy reduction or efficiency schemes need explored now. Relying on market solutions coming along at just the right time is a valid point of view but a tad unrealistic nonetheless.

SBVOR said...


/Sarcasm on/

Come on! Get with the program! Don’t you know that ALL “change” is bad? Don’t you know that the Nanny State must save us from ANY “change”?

Sure, the ONLY constant in the entire universe is “change”. We know that. That’s the point. It’s the perfect solution to the “problem” of how do we continuously grow the Nanny State.

/Sarcasm off/

Dean said...

Andrew -37-

2b includes the phrase "adverse impact" which I consider to be the same as a problem.

2a includes the phrase "continue to be of concern."

Roger - It seems to me that "adverse impatc" is more clear and unambiguous than "continue to be of concern." So this could be another difference between the two. But clearly they both indicate either a problem or a potential problem.

Andrew said...

A single Hypothesis is a single statement. Thus the latter two hypotheses are nothing more and nothing less than:

2a Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and involve a diverse range of first- order climate forcings, including, but not limited to, the human input of carbon dioxide (CO2).

2b Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and are dominated by the emissions into the atmosphere of greenhouse gases, the most important of which is CO2.

Nowhere is either a need for "concern" other than "research" concern or "adverse impacts" actually addressed by the authors. These statements are bluster, that was probably put there due to either a reviewer or several of the authors need to feel secure about supporting "the cause".

Your response will be to say I am a conspiracy theorist. There is no conspiracy when people act out of their own desire to seek happiness. Otherwise one must conclude (I'm sure you do actually) that the whole capitalist system is a vast conspiracy to charge prices for things and create spontaneous evil order!

However, let's be perfectly clear. That the effects of the influences will be of "concern" (which you seem to translate as "worrisome") or "adverse in impact" are separate hypotheses. It is totally incorrect for them to be said to be part and parcel with the rest of the hypotheses to which they are sneakily attached like pretty hard to notice window dressing.

Freedom's Truth said...

What is the boundary between "first-order" and minimal?

The hypothesis suffers from imprecision in quantification.

Should it not be written better as "Climate variability at the decade-by-decade level in the latter 20th and 21st century has been and will be partially man-made and partially natural. The man-made component of variability will be X1-X2% of total variability in the 1950-2100 timeframe. We consider that percentage as likely to be (minimal/significant/dominant)."

What X1 and X2 are is key.

Dano said...


California is enacting policies that presume 2a is accurate, and numerous policy types that advocate land use changes, different farming practices, etc presume 2a is accurate as well.

I could go on with numerous examples of policies that follow the 2a path, but I'm just starting caffeination procedures.



Dano said...

You don't have to post this, Roger.

I commented before skimming comments. Wow. A certain crowd is attracted here, to the seeming exclusion of other crowds. I hope this was your intent.



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